Structure and properties of the YBa2Cu3O7−x/LaAlO3 superlattices

Superconductor/insulator superlattices have been prepared using pulsed laser deposition. Two different [(YBa2Cu3O7−x)n/LaAlO3)m]×N superlattices with N=15 and N=30 have been studied by high resolution electron microscopy. Both supperlattices show a zero resistivity transition at T=82 K and T=86 K, respectively. High resolution transmission electron microscopy leads us to propose two models for the YBa2Cu3O7−x–LaAlO3 interface layers. These models describe the interfaces as a stacking of CuO–AlO layers and BaO–AlO layers. High resolution transmission electron microscopy observations also reveal the presence of antiphase boundaries in the lanthanum aluminate deposited layers. Their formation is attributed to partial stress relaxation in the superlattice.